Color information processing by neurons of the rhesus monkey brain is assessed using three techniques: a. The increment-threshold spectral sensitivity measurement indicates the behavioral sensitivity to color. b. The single neuron extracellular recording from visual areas are simultaneously compared with the behavioral thresholds. c. The use of the metabolic label, C-14-2-Deoxyglucose permits identification of aggregates of color sensitive neurons within the visual cortex. The objectives of this program are: a. To describe the pattern and location within the visual system of color-sensitive neurons; b. To compare the sensitivity of neurons with that of the monkey; c. To describe the role of opponent and non-opponent neurons in spectral sensitivity; and d. To describe and compare the absolute quantum threshold of neurons with that of behavior.